The general goal of this research is to understand the neural mechanisms underlying praxis, that is complex, purposeful motor actions; these mechanisms are largely unknown. For that purpose, rhesus monkeys will be trained to perform tasks commonly used to determine the presence and evaluate the severity of constructional apraxia in brain-damaged people. These tasks include copying simple geometrical figures, constructing objects out of component parts, and route following in a maze. The activity of single cells during task performance will be recorded in key frontal and posterior parietal areas of the cerebral cortex using a 7- microelectrode system. These areas include the motor and dorsal premotor cortex in the frontal lobe and area 2/5, area 5 and the medial intraparietal area in the parietal lobe. These areas are anatomically interconnected and are intimately involved in the visual specification and control of arm movements in space. Therefore, we expect them to be involved in the aforementioned tasks which tap visuospatial and visuoconstructive abilities for their performance. The data to be obtained will be analyzed using uni- and multivariate statistical methods to determine the control of these tasks by single cells and neuronal populations, and to delineate the specific contribution of each one of the cortical areas above to this control. By analyzing normal brain mechanisms, we hope to discover some basic principles of organization underlying praxis, which could lead to an understanding of brain dysfunction in apraxia.